Enhanced fan and fan drive assembly

ABSTRACT

A fan drive assembly including a cooling fan ( 11 ) and a fluid coupling device ( 13 ). The cooling fan includes a fan hub ( 17 ), a spider ( 15 ), and a plurality of fan blades ( 19 ). The coupling device has an output coupling assembly ( 21 ) including a body ( 23 ) and a cover ( 25 ). The body ( 23 ) includes preferably only three mounting portions ( 67 ), each being disposed immediately adjacent an outer periphery of the body. Each of the mounting portions ( 67 ) defines the necessary machining chucking surfaces ( 73 ), and a spider mounting surface ( 75 ) including a pilot surface ( 77 ) engaging the pilot diameter ( 79 ) of the spider ( 15 ). The body ( 23 ) includes cooling fins ( 61 ) covering substantially all of the rearward surface ( 59 ) of the body not covered by the mounting portions. The fan hub ( 17 ) also includes a rearwardly extending air dam portion ( 81 ), limiting localized radial air flow. The fan drive is able to improve the radial air flow through the body cooling fins and achieve substantially greater heat dissipation from the fan drive assembly, thus permitting greater fan speed for a given input speed.

This is a divisional of U.S. patent application Ser. No. 09/756,344,filed Jan. 8, 2001, now U.S. Pat. No. 6,358,810, issued Mar. 19, 2002,which is a continuation of U.S. patent application Ser. No. 09/257,112,filed on Feb. 25, 1999, now U.S. Pat. No. 6,206,639, issued Mar. 27,2001.

BACKGROUND OF THE DISCLOSURE

The present invention relates to fan drive assemblies of the typeincluding a cooling fan and a fan drive, and more particularly, to suchfan drive assemblies wherein the fan drive is of the type in which heatis generated as a result of the transmission of torque within the fandrive, and the ability of the fan drive to dissipate such generated heatrepresents a limiting factor on the torque transmitting capability ofthe fan drive assembly.

Although the present invention may be used with various types andconfigurations of torque transmitting fan drives, it is especiallyadapted for use with fan drive assemblies of the type including aviscous fluid coupling device as the fan drive, and will be described inconnection therewith.

Fan drive assemblies of the type which may benefit from the use of thepresent invention have found several uses, one of the most common ofwhich is in connection with cooling the radiator of a vehicle engine. Asis well known to those skilled in the art, the fan drive of the typicalfan drive assembly comprises a viscous fluid coupling device, so namedbecause the coupling utilizes a high viscosity fluid to transmit torque,by means of viscous shear drag, from an input coupling member (clutch)to an output coupling member (housing), with the cooling fan beingbolted, or otherwise suitably attached, to the output coupling member.

The present invention is especially advantageous when used on arelatively high horsepower fan drive assembly, i.e., one which iscapable of transmitting somewhere in the range of about two to abouttwelve horsepower from the fan drive to the cooling fan. Typically, suchhigh horsepower fan drives include an output coupling member of the typewhich comprises a cast aluminum body and a cast aluminum cover. Theinput coupling member is typically also made as a cast aluminum member,and cooperates with the body and/or the cover to define a plurality ofinterdigitated lands and grooves which define the viscous shear space.When the shear space is filled with viscous fluid, typically a siliconfluid, torque is transmitted from the input coupling member to theoutput coupling assembly, in response to the rotation of the inputcoupling member.

During such torque transmission, substantial heat is generated as aresult of the shearing of the viscous fluid between the lands andgrooves. The amount of heat generated is generally proportional to the“slip speed” of the fan drive, i.e., the difference between the speed ofthe input and the speed of the output. It is generally well understoodby those skilled in the art that the ability to transmit torque islimited by the ability of the device to dissipate the heat generated.For example, in a viscous fan drive, if the temperature of the viscousfluid exceeds a certain maximum temperature, the result will be adeterioration of the viscous properties of the fluid, resulting in agradual loss of the torque transmitting capability of the fluid.

In the fan drive art, it has been conventional for the design anddevelopment of a particular cooling fan to occur generally independentlyof the design and development of the viscous fan drive with which thefan is to be utilized. In other words, the fan is designed to providethe desired operating parameters (e.g., torque, air flow, etc.), thusdetermining the blade configuration and spacing, and then the mountingportion of the fan (the “spider”) is designed or merely modified toadapt to the configuration of the particular fan drive mountingarrangement (e.g., mounting pads or bosses, disposed at a particulardiameter from the axis of the fan drive).

What has not been conventional in the fan drive art is to design thecooling fan and the fan drive as a “package”, with the goal ofmaximizing the heat dissipation of the overall fan drive assembly. As aresult, it would appear that, at the time of the present invention,there is no commercially available fan drive assembly which achievesnearly its optimum, potential heat dissipation (heat rejection). As afurther result, practically every fan drive assembly in commercial useis larger and more expensive than is actually necessary, in order toachieve a particular, desired flow of cooling air through the radiator.

Although the present invention is not limited to a fan drive assembly inwhich the fan is mounted to the rearward side of the housing (body),rather than being mounted to the cover, the invention is especiallyadvantageous in such an arrangement, and will be described in connectiontherewith. A typical “rear mount” fan drive is illustrated and describedin U.S. Pat. No. 4,384,824, in which the body member includes fourmounting bosses located radially inward of the body cooling fins. As aresult, the fan spider interferes with the radial flow of cooling airthrough the body cooling fins, thus reducing the heat dissipationcapability of the particular fan drive assembly.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved fan drive assembly in which the cooling fan and the fluidcoupling device driving the fan are designed such that the overallassembly approaches the optimum, potential heat dissipation.

It is a more specific object of the present invention to provide animproved fan drive assembly in which the cooling fan is mounted to thebody (housing) of the fluid coupling device in a manner whichsubstantially improves the flow of air through the housing cooling fins.

It is a related object of the present invention to provide an improvedfan drive assembly which accomplishes the above-stated objects, and inwhich the cooling fan is configured to further improve the flow of airthrough the housing cooling fins.

It is another object of the present invention to provide an improved fandrive assembly which accomplishes the above-stated .objects, and inwhich the cover cooling fins are configured to improve the flow of airthrough the cover cooling fins.

The above and other objects of the invention are accomplished by theprovision of a fan drive assembly of the type comprising a cooling fanattached to a fluid coupling device, the cooling fan comprising a fanhub, a spider portion, and a plurality of fan blades extending radiallyfrom the fan hub. The fluid coupling device comprises a first rotatablecoupling assembly including a body member having a rearward surface, anda cover member cooperating with the body member to define a fluidchamber therebetween, a second rotatable coupling member being disposedin the fluid chamber for rotation relative to the first couplingassembly. The first coupling assembly and the second coupling membercooperate to define a viscous shear chamber therebetween, whereby torquemay be transmitted from the second coupling member to the first couplingassembly in response to the presence of viscous fluid in the shearchamber. The body member includes a plurality of cooling fins and aplurality of mounting portions, the spider portion being attached to themounting portions and defining a pilot diameter.

The improved fan drive assembly is characterized by the body memberincluding a plurality of mounting portions, each of which is disposedimmediately adjacent an outer periphery of the body member. Each of themounting portions defines a machining chucking surface, and a spidermounting surface on a rearward face thereof. The spider mounting surfaceincludes a pilot surface in engagement with the pilot diameter of thespider portion. The plurality of cooling fins covers substantially allof the rearward surface of the body member not covered by the mountingportions.

In accordance with another aspect of the present invention, the fan huband each of the plurality of fan blades cooperate to define a rearwardaxially extending air dam portion operable to restrict localized radialair flow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross-section of one-half of the fan drive assemblyof the present invention, taken on line 1—1 of FIG. 3, but on a largerscale than FIG. 3, and including the cooling fan.

FIG. 2 is an axial cross-section of one-half of the fan drive assemblyof the present invention, taken on line 2—2 of FIG. 3, and on the samescale as FIG. 1, but also including the cooling fan.

FIG. 3 is a plane view, looking toward the left in FIGS. 1 and 2,showing only the body member of the fluid coupling device whichcomprises part of the present invention.

FIG. 4 is a schematic, fragmentary view of a portion of the body memberand fan spider, illustrating one aspect of the present invention.

FIGS. 5A and 5B are schematic, fragmentary views, similar to FIG. 4,illustrating the flow of cooling air over the body, comparing the “PRIORART” and the “INVENTION”, respectively.

FIG. 6 is a fragmentary, axial cross-section through the cooling fan,illustrating one additional aspect of the present invention.

FIG. 7 is a schematic, fragmentary view of a portion of the cover,illustrating another aspect of the present invention.

FIG. 8 is a graph of Fan Speed (in RPM) versus Input Speed (in RPM),comparing the Prior Art (Baseline) coupling device and the Enhancedassembly of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, which are not intended to limit theinvention, FIGS. 1 and 2 illustrate one preferred form of a fan driveassembly made in accordance with the present invention. The fan driveassembly comprises a cooling fan, generally designated 11, and a fluidcoupling device, generally designated 13, the function of which is toprovide drive torque to the cooling fan 11.

The cooling fan 11 may, within the scope of the present invention, havevarious configurations and constructions, and the invention is notlimited to the particular construction shown, except as is specificallynoted otherwise hereinafter. The cooling fan 11 comprises a stampedannular metal spider 15, which is usually a relatively thin, flat,sheet-like member. Preferably, an annular plastic hub portion 17 ismolded about the outer periphery of the spider 15. However, the use ofterms like “spider” and “hub” should not be construed as implyingstructural limitations. For example, within the scope of the presentinvention, the spider 15 could be molded integrally with the hub portion17. Typically, there is a plurality of fan blades 19 molded integrallywith the hub portion 17, the fan blades 19 being shown onlyfragmentarily in FIGS. 1 and 2. It should be understood that theparticular arrangement and configuration of the fan blades 19 also doesnot constitute an essential aspect of the invention. As a furtherexample, the fan 11 may be of either the “ring fan” type, in which anannular ring surrounds the outer tips of the fan blades 19, or the “openfan” type, in which no ring surrounds the fan blades. Other details ofthe cooling fan 11 will be described subsequently.

The fluid coupling device 13 typically includes an output couplingassembly 21 including a diecast aluminum housing (body) member 23, and adiecast aluminum cover member 25. Typically, the body 23 and cover 25are secured together such as by a rollover of the outer periphery of thecover 25. However, in some coupling devices, the body and the cover arebolted together.

The body 23 and cover 25 cooperate to define a fluid chamber, anddisposed therein is an input coupling member 27. As is well known in theart, the fluid coupling device 13 is adapted to be driven by a liquidcooled engine (not shown). The device includes an input shaft 29 onwhich the input coupling member 27 is mounted. The input shaft 29 isrotatably driven, typically by means of a flange 31 which may be boltedto the mating flange of an engine water pump (also not shown). The inputshaft 29 functions as a support for the inner race of a bearing set 33,which is seated on the inside diameter of the body 23. The forward end(left end in FIGS. 1 and 2) of the input shaft 29 has an interferencefit between a serrated portion and an opening defined by a hub portion35 of the input coupling member 27. As a result, rotation of the inputshaft 29 causes rotation of the input coupling member 27.

The body 23 and the cover 25 cooperate to define a fluid chamber, asmentioned previously, which is separated, by means of a circular valveplate 37 into a fluid operating chamber 39 and a fluid reservoir chamber41. Thus, it may be seen that the input coupling member 27 is disposedwithin the fluid operating chamber 39.

The cover 25 defines a raised, annular reservoir-defining portion 43,which is disposed to be generally concentric about an axis of rotation Aof the device. The cover 25 further defines a generally cylindricalshaft support portion 45, and rotatably disposed within the shaftsupport portion 45 is a valve shaft 47, extending outwardly (to the leftin FIGS. 1 and 2) through the cover 25. Attached to the inner end (theright end in FIGS. 1 and 2) of the valve shaft 47 is a valve arm 49.Movement of the valve arm 49 controls the flow of fluid from thereservoir chamber 41 to the operating chamber 39 through a fill opening(port) 51 formed in the valve plate 37, and shown only in FIG. 2.

Operatively associated with the outer end of the valve shaft 47 is atemperature-responsive bimetal element, which in the subject embodiment,and by way of example only, comprises a coil member 53. The manner inwhich the bimetal coil 53 operates to control the movement of the valvearm 49, in response to variations in ambient air temperature, is wellknown in the art, forms no part of the present invention, and will notbe described further herein.

Although not shown herein in either FIG. 1 or FIG. 2, it is typical, andwell known to those skilled in the art, for the cover 25 to define fluidpassages communicating from the outer periphery of the operating chamber39 back to the reservoir chamber 41. Typically, the cover 25 would beprovided with a wiper element (also not shown herein) whereby fluidwould be pumped from the operating chamber 39, through the fluidpassages and back into the reservoir chamber 41, in response to relativerotation between the input coupling member 27 and the cover 25. Thispump (scavenge) function is also well known in the art, forms no directpart of the present invention, and will not be described further herein.

In the subject embodiment, and by way of example only, the inputcoupling member 27 includes a forward surface which defines a pluralityof annular lands 55. The adjacent surface of the cover 25 forms aplurality of annular lands 57. The annular lands 55 and 57 areinterdigitated to define a serpentine-shaped viscous shear chambertherebetween. The operation of the fluid coupling device 13 may bebetter understood by reference to U.S. Pat. No. 4,974,712, assigned tothe assignee of the present invention and incorporated herein byreference. Briefly, when torque is transmitted from the vehicle engineby means of the input shaft 29 to the input coupling member 27, theresult is a shearing of the viscous fluid contained in the shear spacebetween the annular lands 55 and 57, the shear space also being referredto hereinafter by the reference numeral 58.

Referring still to FIGS. 1 and 2, but now also to FIGS. 3 and 4, oneaspect of the present invention will be described. The body 23 defines arearward surface 59 (shown best in FIGS. 2 and 3). The cast body 23 alsoincludes a plurality of cooling fins, generally designated 61 andpreferably cast integrally with the body 23, the fins 61 extendingaxially rearward (to the right in FIGS. 1 and 2). Each of the coolingfins 61 includes a radially outer fin portion 63 and a radially innerfin portion 65, it being understood that, as may best be seen in FIG. 3,the fin portions 63 and 65 together comprise a single, integral fin, andthe primary difference between the portions 63 and 65 is that the outerfin portion 63 has an axial height H1 (measured from the rearwardsurface 59) and the inner fin portion 65 has an axial height H2, as maybest be seen in FIG. 4.

Referring now primarily to FIGS. 1 and 3, the body 23 also includes aplurality of mounting portions or bosses 67. Each boss 67 defines aninternally threaded bore 69, by means of which the metal spider 15 maybe attached to the respective boss 67, preferably by means of a bolt 71.Reference is made hereinafter, and in the appended claims, to a“plurality” of the mounting portions 67. Preferably, there are onlythree of the mounting portions, for reasons of improved heatdissipation, as will become apparent from the subsequent description.However, in some applications of the present invention, especially whenusing relatively high torque fans, it may be necessary to utilize fourof the mounting portions 67, and it should be clearly understood thateither alternative is within the scope of the invention.

Referring still primarily to FIGS. 1 and 3, each of the mounting bosses67 is disposed immediately adjacent the outer periphery of the body 23,which as is best shown in FIG. 3, has an outside diameter D1. Eachmounting boss 67 includes, on its outer periphery, a machining chuckingsurface 73, illustrated herein, by way of example only, as being asubstantially flat surface, including a small notched portion orientedparallel to the axis A of the coupling device 13. As is well known tothose skilled in the art, the chucking surfaces 73 are included topermit the body 23 to be chucked, or held stationary, while the varioussurfaces and diameters are machined. It should be understood that thepurpose of the invention is still accomplished in the chucking surfacesare disposed on the radially inner portion of each of the mountingbosses 67. In the subject embodiment, the three machining chuckingsurfaces 73 define a diameter D2, which is preferably at least 90-95% ofthe diameter D1. It has been conventional in the viscous fluid couplingart, in which the cooling fan is to be mounted relative to the body, forthe body to include three chucking portions and three or four fanmounting bosses. In other words, there would be a total of six or sevendifferent structural elements on the rearward surface of the body whichwould represent a discontinuation of, or an interference with, thepresence of cooling fins and the radial flow of cooling air over therearward surface of the body.

It is one important aspect of the present invention to recognize theimportance of the radial flow of cooling air over the body 23 as afactor in the overall heat dissipation capability of the fan driveassembly. Therefore, as one important structural feature of the presentinvention, the functions of machining chucking and fan mounting havebeen combined into a single structure. Each of the mounting bosses 67also includes a flat, transverse spider mounting surface 75, againstwhich a forward surface of the spider 15 is disposed, and a generallyannular pilot surface 77. As the name implies, the function of the pilotsurface 77 is to “pilot” or to locate accurately an inside pilotdiameter 79 (see FIGS. 2 and 4) of the spider 15. The pilot surfaces 77define a diameter D3, and in the course of the development of thepresent invention, it has been determined that heat dissipation ismaximized whenever the diameter D3 is in the range of about 53% to about83% of the diameter D1. In the subject embodiment, and by way of exampleonly, the diameter D3 is about 72% of the diameter D1.

In accordance with another important aspect of the present invention,and as may best be seen in FIG. 3, the mounting portions 67 and thevarious surfaces 73, 75, and 77 are made as small as possible,consistent with the function they are to perform, with substantially allof the remainder of the rearward surface 59 being covered by the coolingfins 61. Those skilled in the art will understand that the rearwardsurface 59 refers to the generally transverse surface radially outwardof the generally frusto-conical portion of the body 23 which surroundsthe bearing set 33. Thus, it may be seen that, in terms of the mountingportions 67 and cooling fins 61, it is possible for air to flow radiallyover nearly all of the rearward surface 59 of the body 23, thusmaximizing the area on the rearward surface 59 which is actuallyavailable to achieve heat dissipation.

Referring now primarily to FIGS. 2, 3 and 4, another important aspect ofthe present invention relates to the outer and inner fin portions 63 and65. As may best be seen in FIG. 2, and as is generally well known tothose skilled in the viscous fluid coupling art, the heat generationwithin the viscous shear space 58 is greater toward the radially outerextent, and less toward the radially inner extent. Therefore, the outerfin portions 63, having the axial height H1 as described previously,have a radial extent which corresponds approximately to the region ofgreatest heat generation, and therefore, the region of the greatest needfor heat dissipation. Radially inward from the fin portions 63, theinner fin portions 65, having the axial height H2, have substantiallyless heat dissipation capability than do the fin portions 63. However,the inner fin portions 65 are radially aligned with a region in whichsubstantially less heat is generated, and therefore, less heatdissipation is required. In addition, it has been determined, inconnection with the development of the present invention, that therelatively reduced axial height of the fin portions 65 has one furtheradvantage, to be described subsequently.

Referring now primarily to FIGS. 5A and 5B, which are air flow diagrams,it should be understood that the length of each of the arrows indicatesflow velocity, i.e., the shorter arrows representing relatively lowervelocities, and the longer arrows representing relatively highervelocities. FIGS. 5A and 5B were generated using well known and widelyaccepted CFD (computational fluid dynamics) analysis techniques. In FIG.5A, the PRIOR ART, with the spider extending almost as far in radiallyas the frusto-conical portion of the body, actually has radially outwardair flow through the region of the cooling fins on the body. However, itmay be seen that the air flow velocity is not especially high, and theoverall heat dissipation by the PRIOR ART assembly reflects therelatively poorer air flow through the body fins.

As may best be seen in FIGS. 2 and 4, the radial extent, inwardly, ofthe outer fin portions 63 corresponds approximately to the radiallyinner extent of the spider 15. Therefore, and as may best be seen inFIG. 5B, having the spider 15 disposed axially adjacent the radiallyouter fin portions 63 serves to direct or constrain air flow radiallyinward through the fin portions 63, to maximize heat transfer from thefin portions 63, as may be seen by the air flow velocity arrows throughthe body cooling fins. After flowing radially inward through the finportions 63, some of the air then flows radially inward through theinner fin portions 65, and then is deflected axially, while some of theair exiting the outer fin portions 63 flows into the open area axiallyabove the inner fin portions 65. The axial height H2 of the inner finportions 65 being substantially less than the axial height H1 makes itpossible for some of the air exiting the fin portions 63 to flowgenerally circumferentially relative to the fins, before flowingrearward (to the right in FIG. 2), thus reducing the overall restrictionto air flow and further improving heat transfer from the outer finportions 63.

Referring now primarily to FIGS. 2 and 4, it may be seen that a forwardsurface of the spider 15 defines an axial height H3 from the rearwardsurface 59 of the body 23. Preferably, the axial height H1 of each ofthe outer fin portions 63 is somewhat less than the axial height H3, butnot enough to provide a major air flow path between the “top” of eachfin portion 63 and the adjacent surface of the spider 15, which would ineffect represent a “leak” path for air, rather than forcing the airthrough the fin portions 63 as described previously. On the other hand,it would not be desirable for the spider 15 to be engaging the finportions 63, assuming normal casting tolerances for the fin heights,because of the possibility of one of the fins portions 63 extending“above” an adjacent spider mounting surface 75, and preventing the fanspider 15 from piloting properly.

Referring now primarily to FIGS. 2 and 6, the annular plastic hubportion 17 includes a rearward, axially extending air dam portion 81,preferably molded integrally with the hub portion 17. Although thepresent invention is not limited to any particular radial location ofthe air dam portion 81, it is preferably located radially inward of thefan blades 19. As was mentioned in the BACKGROUND OF THE DISCLOSURE, oneimportant aspect of the present invention is to design the fan 11 andthe fluid coupling 13 as a package, and the provision of the air damportion 81 is another example of that design approach. It has beendetermined, during the development of the present invention, that thepresence of the axially extending air dam portion 81 is beneficial inincreasing heat dissipation from the body 23, indicating that the airdam portion 81 improves the flow of cooling air over the cooling fins61. This improvement is illustrated in FIG. 5B, wherein it may beobserved that the air flow velocity radially inward from the air damportion 81 is extremely low, which is believed to be related to theobservable improvement in air flow velocity both through the bodycooling fins and through the fan blades.

Referring now primarily to FIG. 6, a significant dimension of the fan isthe PW (projected width) of the fan blade 19, i.e., the width the bladeappears when viewed in the circumferential direction, rather than whenviewed in the “normal” direction, relative to the blade. In FIG. 6,there is also illustrated a dimension referred to as “BF” (i.e., thedistance from the back of the blade PW to the front surface of thespider, the surface to be attached to the mounting portions). Then thereis a dimension referred to as “BB” (i.e., the distance from the back ofthe blade PW to the back surface of the spider, or BF minus thethickness of the spider). The air dam portion 81 defines an axial lengthL, measured from the rear surface of the spider. It should be understoodthat the measurement of the length L is not necessarily extremelyprecise. During the development of the subject embodiment, it wasdetermined that, as the length L of the portion 81 is varied, the heatdissipation from the body 23 is maximized when the length L is in therange of about 60% to about 70% of the back-to-back dimension BB.

Referring still primarily to FIG. 6, it should be noted that the hubportion 17 is fairly short, in the axial direction, and is much shorterin the axial direction than PW, the projected width of the fan blades19. It is believed that the more conventional, wider hub portion has theeffect of restricting the radial flow of air. In connection with thedevelopment of the subject embodiment, it has been observed that,although the air dam portion 81 limits radial air flow, and therebyimproves heat dissipation, the elimination of a major part of the axiallength of the hub portion also improves heat dissipation. It is believedthat, with a rear mounted fan as shown herein, reducing the axial lengthof the hub portion, forward of the spider, improves the radial inwardair flow over the cooling fins 61, as is shown in FIG. 5B. On the otherhand, and as explained previously, restricting radial air flow on therearward side of the spider has been found to help the radial flow ofcooling air over the fins 61. Optimum radial inward air flow over thecooling fins has been found to occur where the axial length of the hubportion is in the range of 25% to 40% of the fan blade projected widthPW.

Referring again primarily to FIGS. 1 and 2, but also to FIG. 7, it maybe seen that the cover 25 defines a forward surface 83 and a pluralityof cooling fins, generally designated 85, preferably cast integrallywith the cover 25. Each of the cooling fins 85 includes a radially outerfin portion 87 and a radially inner fin portion 89. In a mannergenerally similar to that described for the body 23, each of the outerfin portions 87 defines an axial height H4, measured axially from theforward surface 83, and each of the inner fin portions 89 has an axialheight H5, the height H4 being substantially greater than the height H5.The higher, radially outer fin portions 87 are disposed immediatelyforward of the land and groove area 55,57, and therefore, for the samereasons described in connection with the fins 61, the fin portions 87are much higher to achieve much greater heat dissipation, exactly whereit is needed.

In accordance with another feature of the invention, and to furtherimprove the heat dissipation of the fin portions 87, an annularplate-like member 91 is provided in engagement with the tip portions ofthe fin portions 87. Preferably, the plate-like member 91 is relativelythin, perhaps even being thin enough to be somewhat deformable uponassembly, wherein the member 91 may simply be pressed into an annularchannel 93 formed in the tips of the fin portions 87 Preferably, theannular channel 93 would be used “as cast”, so that the feature would beessentially “free” in terms of manufacturing expense. It is believedthat the presence of the annular member 91 has the effect of directingair flow through the cooling fins 85, and more specifically,constraining air flow within the fin portions 87, thereby maximizingheat transfer from the fin portions in much the same way as the spider15 does in connection with the cooling fins 61. This aspect of theinvention is also illustrated in the air flow diagram of FIG. 5B.

In connection with the development and testing of the present invention,it has been determined that each of the individual features, illustratedand described herein, contributes positively to the heat dissipation ofthe fan and fan drive assembly. In addition, the individual featureshave been “optimized” so that the overall fan and fan drive assemblyachieves the nearly optimum heat dissipation. This improvement isillustrated in the graph of FIG. 8, which is a graph of Fan Speed (inRPM) versus Input Speed (also in RPM). The graph labeled “PRIOR ART”represents what was considered a “baseline” unit, which was the Series565 fan drive assembly, sold commercially by the assignee of the presentinvention. The graph labeled “INVENTION” represents the identical fanand fan drive assembly, except for the various features illustrated anddescribed herein.

In conducting the testing shown in the graph of FIG. 8, each of sevenfan drive assemblies received a continuous input speed of 4000 RPM (andat a constant elevated temperature of the surrounding air), initially,and then the input speed was increased to 4100 RPM for about half anhour. Then the input speed was dropped back down to 4000 RPM for a brief“rest period”, after which the input speed was increased to 4200 RPM.This process of alternating rest periods (at 4000 RPM) and increasinginput speeds was repeated until each fan drive assembly “deteriorated”in its performance to the point at which its output speed (Fan Speed)had “drooped” or decreased ten percent from the initial fan speed,during a rest period.

Several observations may be made about the performance of the presentinvention, and the results of the substantially improved heatdissipation resulting from the invention (enhanced assembly). First, theaverage fan speed for the enhanced assembly was at least about 150 RPMhigher than for the baseline assembly, even before droop occurred, i.e.,from the initial 4000 RPM input speed until the input speed reachedabout 4600 RPM. Secondly, for the baseline assembly, droop occurred at4900 RPM, i.e., above that input speed, performance of the assemblywould not be considered acceptable. In the case of the invention, thedroop did not occur until the input speed reached about 5300 RPM, andeven then the assembly of the present invention still was capable ofproviding a fan speed of nearly 2900 RPM whereas, when the baseline unitdrooped at 4900 RPM input speed, its fan speed was already down to justover 2700 RPM. As is well known to those skilled in the art, it isimportant to keep the viscous fluid relatively cooler, because theviscosity then remains at a higher level, which accounts for theincreased fan speed for a given input speed. Thus, the empirical datashowing the higher fan speed for any given input speed tends to provethe hypothesis above that the present invention results in substantiallygreater heat dissipation, i.e., the viscous fluid remains cooler.

Another advantage of the invention relates to the number of cooling fins61 (see FIG. 3). As a result of the improved air flow over the bodycooling fins 61, it has been determined as part of the development ofthe subject embodiment that the number of fins 61 can be decreased, fromover 60 to only 42, without a loss of heat dissipation. The reduction inthe number of fins made it possible to improve the integrity of the bodydie casting, and at the same time, reduce the overall weight of thebody.

The invention has been described in great detail in the foregoingspecification, and it is believed that various alterations andmodifications of the invention will become apparent to those skilled inthe art from a reading and understanding of the specification. It isintended that all such alterations and modifications are included in theinvention, insofar as they come within the scope of the appended claims.

What is claimed is:
 1. A fan drive assembly of the type comprising acooling fan attached to a fluid coupling device, said cooling fancomprising a fan hub, a spider portion and a plurality of fan bladesextending radially from said fan hub, said fluid coupling devicecomprising a rotatable coupling assembly including a body member havinga rearward surface, and a cover member cooperating with said body memberto define a fluid chamber therebetween, a rotatable coupling memberdisposed in said fluid chamber for rotation relative to said couplingassembly; said coupling assembly and said coupling member cooperating todefine a viscous shear chamber therebetween, whereby torque may betransmitted from said coupling member to said coupling assembly inresponse to the presence of viscous fluid in said viscous shear chamber;said body member including a plurality of cooling fins and a pluralityof mounting portions, said spider portion being attached to saidmounting portions and defining a pilot diameter; characterized by: (a)said body member including only three of said mounting portions, each ofwhich is disposed immediately adjacent an outer periphery of said bodymember; (b) each of said mounting portions including a spider mountingsurface on a rearward face thereof, said spider mounting surfaceincluding a radially disposed pilot surface in engagement with saidpilot diameter of said spider portion; (c) said plurality of coolingfins covering substantially all of said rearward surface of said bodymember not covered by said mounting portions; and (d) said body memberdefining an outside diameter, and said spider portion pilot diameterdefining a diameter which is from about 53% to 83% of said outsidediameter.
 2. A fan drive assembly comprising: a cooling fan including aspider portion, a hub mounted to said spider portion and a plurality ofblades extending radially from said hub, said spider portion having acentral opening defining a pilot diameter; a body member having arearward surface with a plurality of mounting portions formed thereon,each of said mounting portions defining an annular spider mountingsurface and a radially disposed pilot surface configured to contact saidpilot diameter, each of said plurality of mounting portions defining anouter periphery and a machine chucking surface at said outer periphery;a means for attaching said spider portion to said plurality of mountingportions with said spider portion contacting said annular mountingsurface and said pilot diameter in engagement with said pilot surface;and a coupling member engagable between said body member and a source ofrotational motion to transmit torque to said body member, therebyrotating said cooling fan.
 3. A fan drive assembly comprising: a coolingfan including a spider portion, a hub mounted to said spider portion anda plurality of blades extending radially from said hub, said spiderportion having a central opening defining a pilot diameter; a bodymember having a rearward surface with a plurality of mounting portionsformed thereon, each of said mounting portions defining an annularspider mounting surface and a radially disposed pilot surface configuredto contact said pilot diameter, each of said plurality of mountingportions defining an outer periphery and a machine chucking surface atsaid outer periphery, said outer periphery of said plurality of mountingportions being circular and said machine chucking surface being linear;and a means for attaching said spider portion to said plurality ofmounting portions with said spider portion contacting said annularmounting surface and said pilot diameter in engagement with said pilotsurface; and a coupling member engagable between said body member and asource of rotational motion to transmit torque to said body member,thereby rotating said cooling fan.